In a speech in Washington Thursday, Transportation Secretary Elaine Chao said U.S. aviation regulators have no timeline for returning the Boeing 737 Max to service.

Southwest Airlines is joining two other U.S. airlines in removing Boeing 737 Max flights from its schedule through Nov. 2, reinforcing its decision to postpone hiring new pilots and promoting existing ones.

The extension will take out about 180 daily flights from Dallas-based Southwest's schedule, the company said Thursday. That's about 30 more daily flights than previous estimations.

"By proactively removing the Max from scheduled service, we can reduce last-minute flight cancellations and unexpected disruptions to our customers' travel plans," Southwest said in a statement.

The company has also postponed two of its new-hire pilot classes and two captain upgrade classes until airlines have more details on the return of the Max, essentially freezing hiring and promotions for the time being.

Max jets have been grounded worldwide since March, after the second of two crashes in Indonesia and Ethiopia that led to 346 deaths.

Southwest had previously canceled flights through Oct. 1, although CEO Gary Kelly told employees in a company-wide message that it could take "well beyond" that to get the aircraft back into service.

Earlier this week, American Airlines canceled Max flights through Nov. 2. United Airlines removed the planes through Nov. 3.

Southwest operated 34 Max jets when the FAA grounded the planes in March, but was scheduled to get another 44 planes during 2019.

In a speech in Washington Thursday, Transportation Secretary Elaine Chao said U.S. aviation regulators have no timeline for returning the Max to service and won't act until they are sure it is safe.

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The Federal Aviation Administration has to be assured that a fix being developed by Boeing will prevent any future accidents, she said.

"The FAA will lift the aircraft's prohibition order when it is deemed safe to do so," Chao said. "That is the bottom line: There is no timeline."

Chao was speaking before the Air Line Pilots Association's Air Safety Forum. ALPA is the largest pilot's union in North America.

Boeing is altering software on the plane that had malfunctioned in both accidents, pushing each plane's nose down without pilot input. The crews weren't able to counter the plane and they lost control.

FAA is also developing new training requirements for pilots on the 737 Max, Chao said. A technical advisory board including experts from NASA and the Air Force is also weighing in on the decision, Chao said.

The attempt to adapt the software on the Maneuvering Characteristics Augmentation System, which has been identified as a factor in crashes in Indonesia and Ethiopia, has been slower than was initially predicted.

In recent weeks, the FAA identified a new potential flaw linked to how the plane responds during a failure of a flight computer on the plane. Boeing has said that it can address the problem with a separate software patch.

Dom DiFurio. Dom is a staff writer covering breaking business news. He writes about the companies and transactions that shape life in North Texas. Dom considers himself among the many transplants that moved to Texas from the crowded coasts who found more than enough reasons to call it home.